Thermoplastic Composite Materials Approach for More Circular Components: From Monomer to In Situ Polymerization, a Review

Abstract

To move toward eco-sustainable and circular composites, one of the most effective solutions is to create thermoplastic composites. The strong commitment of world organizations in the field of safeguarding the planet has directed the research of these materials toward production processes with a lower environmental impact and a strong propensity to recycle the polymeric part. Under its chemical properties, Nylon 6 is the polymer that best satisfies this specific trade-off. The most common production processes that use a thermosetting matrix are described. Subsequently, the work aimed at investigating the use of thermoplastics in the same processes to obtain comparable performances with the materials that are currently used. Particular attention was given to the in situ anionic polymerization process of Nylon 6, starting from the ε-caprolactam monomer. The dependencies of the process parameters, such as temperature, time, pressure, humidity, and concentration of initiators and activators, were therefore investigated with reference to the vacuum infusion technique, currently optimized only to produce thermosetting matrix composites, but promising for the realization of thermoplastic matrix composite; this is the reason why we chose to focus our attention on the vacuum infusion. Finally, three production processes of the polymeric matrix and glass fiber composites were compared in terms of carbon footprint and cumulative energy demand (CED) through life-cycle assessment (LCA).

Different Production Processes for Thermoplastic Composite Materials: Sustainability versus Mechanical Properties and Processes Parameter

“…There are two process techniques to manufacture thermoplastic composite parts: reactive and melt processing. The first solution focuses on in-situ polymerization, starting from water-like viscosity monomers that could potentially provide an optimal reinforcement impregnation, and a subsequent polymerization reaction triggered by temperature increase [ 7 ]. The second one lies in melt processing, discussed in detail in this article.…”

“…As Figure 1 shows, in the general context of thermoplastic polymer matrix composite manufacturing, two approaches can be taken: the most direct, Reactive Processing, which starts from the fabric impregnation with the monomer and involves in-situ polymerization. We will not discuss this process in this paper as it has been addressed and explored in detail in another work [ 7 ] by our research group. Instead, our attention will be focused, in this article, on the second technique, Melt Processing.…”

Development of single‐stream resin transfer molding using in‐situ anionic polymerization of ε‐caprolactam with preprocessing on carbon fibers

“…[6][7][8] To overcome these issues, researchers have studied thermoplastic resin transfer molding (T-RTM). 9 T-RTM utilizes anionic ring-opening polymerization of ε-caprolactam (CPL), which is a monomer of A-PA6. CPL is a cyclic structure that undergoes a type of chain growth polymerization by the addition of CPL is carried by one end of the polymer chain.…”

Carbon-Fiber-Recycling Strategies: A Secondary Waste Stream Used for PA6,6 Thermoplastic Composite Applications

“…Currently, the main ways for the disposal of composite waste are incineration and landfilling, but these strategies will no longer be adequate due to environmental pollution and loss of CFs with high added value [2]. Recently, several recycling technologies have been proposed to treat composite materials with CFs and recover the CFs to reuse them in other applications for both economic and environmental reasons, aiming at the production of sustainable composites made with recycled reinforcement and a recyclable matrix [4]. The main technologies explored so far include mechanical recycling (shredding, crushing, milling), chemical recycling (solvent, catalyst, or supercritical fluids), and thermal recycling (pyrolysis, oxidation, steam thermolysis), and the objective of these techniques is to recover CFs under conditions as close to their initial state as possible to facilitate reuse in other applications [5].…”